78 lines
2.0 KiB
C
78 lines
2.0 KiB
C
/* Support routines for the intrinsic power (**) operator.
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Copyright (C) 2004-2020 Free Software Foundation, Inc.
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Contributed by Paul Brook
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This file is part of the GNU Fortran 95 runtime library (libgfortran).
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Libgfortran is free software; you can redistribute it and/or
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modify it under the terms of the GNU General Public
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License as published by the Free Software Foundation; either
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version 3 of the License, or (at your option) any later version.
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Libgfortran is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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Under Section 7 of GPL version 3, you are granted additional
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permissions described in the GCC Runtime Library Exception, version
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3.1, as published by the Free Software Foundation.
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You should have received a copy of the GNU General Public License and
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a copy of the GCC Runtime Library Exception along with this program;
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see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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<http://www.gnu.org/licenses/>. */
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#include "libgfortran.h"
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/* Use Binary Method to calculate the powi. This is not an optimal but
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a simple and reasonable arithmetic. See section 4.6.3, "Evaluation of
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Powers" of Donald E. Knuth, "Seminumerical Algorithms", Vol. 2, "The Art
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of Computer Programming", 3rd Edition, 1998. */
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#if defined (HAVE_GFC_INTEGER_16) && defined (HAVE_GFC_INTEGER_4)
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GFC_INTEGER_16 pow_i16_i4 (GFC_INTEGER_16 a, GFC_INTEGER_4 b);
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export_proto(pow_i16_i4);
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GFC_INTEGER_16
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pow_i16_i4 (GFC_INTEGER_16 a, GFC_INTEGER_4 b)
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{
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GFC_INTEGER_16 pow, x;
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GFC_INTEGER_4 n;
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GFC_UINTEGER_4 u;
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n = b;
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x = a;
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pow = 1;
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if (n != 0)
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{
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if (n < 0)
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{
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if (x == 1)
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return 1;
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if (x == -1)
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return (n & 1) ? -1 : 1;
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return (x == 0) ? 1 / x : 0;
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}
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else
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{
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u = n;
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}
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for (;;)
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{
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if (u & 1)
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pow *= x;
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u >>= 1;
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if (u)
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x *= x;
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else
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break;
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}
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}
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return pow;
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}
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#endif
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